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the ground -water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. First ground water is predicted at 118 to 129 feet below ground surface for this Site; consequently, significant nitrate reduction would be anticipated as the septic effluent percolates downward. Clay -containing soils, like those found on this Site, also tend to inhibit downward movement of nitrate due to adsorption of the nitrate ions to the soil. Sources of Nitra Dairies, orchards that require fertilization in sandy soils, and septic systems have been found to be the most significant sources of nitrate in ground water. Three dairies are located within one-third of a mile of the Site; however, based on the nitrate map reviewed, the dairies do not appear to have caused an elevation of nitrate levels in the area above the MCL. Percolating Recharge Waters One of the most determinant factors in the Hantzsche and Finnemore equation is the rate of recharge from percolating waters, which mix with the downward -percolating effluent generated by on-site septic systems. In the original Hantzsche and Finnemore paper, "average recharge rate of rainfall" was utilized. Based on San Joaquin County Environmental Health Department policy (personal communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore equation should be derived from average monthly precipitation of rainfall and evapotranspiration rates for the area; the data should be obtained from the California Irrigation Management Information System (CIMIS). Recharge is calculated by first determining whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is the percolating recharge water into the aquifer. Runoff and stream infiltration drainage are not factored into the calculation. This approach likely under -estimates recharge to the aquifer and, consequently, over-estimates nitrate loading. The Site is located between the CIMIS stations at Staten Island (station 242) and Holt (station 248); taking both stations into account will yield a value more representative of the Site area. Data for the Staten Island station were available for 2016 through 2021; based on the calculation shown, the estimated rate of recharge from percolating waters for the Staten Island station is determined to be 8.41 inches (Plate 12). A statistical error of 80 percent is associated with this value. Data from the Holt station were available for 2017 through 2021; based on the calculation shown, the estimated rate of recharge from percolating waters for the Holt station is determined to be 3.07 inches LOGE 2203 Page 9